Most melee weapons that take two weapon slots also have unwieldy, so require two hands to use, but this is not always the case. Power fist only takes one slot but two hands and the SLHG Assault Ram takes two weapon slots but does not have unwieldy, so does it not require two hands to use in melee? can you use it with a sidearm for example?

No, never. N22 gave a 2nd type of power fist for squats (same name, different cost and stats, no unwieldy). So there's that. In olden times, many space marine power fists got converted to Necromunda to show dominance as the top brutal weapon. Today, there are so many close combats weapons in all ranges of power and cost, so power fist is more obscure now and probably not the best pick in terms of competitiveness. The only official character with a power fist is the squat claim jumper, and it has the non-unwieldy squat variant.

